Starting apparatus for electric discharge devices



arch R3,, 11934. L. J. BUTTOLPH 3 L STARTING APPARATUS FOR ELECTRICDISCHARGE DEVICES Filed April 29, 1929 11V VENTOR Patented Mar. 13, 1934PATENT OFFICE UNITED STATES,

STARTING APPARATUS FOR ELECTRIC DISCHARGE DEVICES Application April 29,1929, Serial No. 359,125

7 Claims. (01. 176-124) The present invention relates to gaseousdischarge devices, and particularly to those devices of this type whichare designed to operate with a hot cathode.

The particular object of the invention is to improve the starting andoperation of such devices, but other objects and advantages will beapparent from the following detailed description of two forms ofapparatus embodying my invention or from an inspection of theaccompanying drawing.

The invention consists in certain new and novel features of constructionand combinations of parts hereinafter set forth and claimed.

Gas or vapor discharge devices of low voltage type are commonly providedwith means for impressing a high voltage surge of short duration uponone of their electrodes in order to initiate a discharge when starting,and also in some cases have means for heating the cathode in order tofacilitate starting. In such cases the application of the high potentialto the electrodes before the cathode has had time to heat up isinjurious, as, if a discharge is started before the cathode has reachedthe proper temperature for free emission of electrons, the discharge isconfined to one spot on the cathode, and tends to disintegrate theelectron emitting material. The present invention is for an apparatus todelay the initial application of the high potential until the cathodehas reached the operating temperature. By using the cathode itself toproduce the delay the exact lag necessary is obtained regardless ofambient temperature, or any other variable conditions.

In the accompanying drawing there is shown for purposes of illustrationone form of apparatus embodying the invention, together with amodification thereof, in which Fig. 1 is a schematic diagram of agaseous discharge device partly-in section, and its connection to theassociated apparatus,

Fig. 2 is an end view of the cathode shown in Fig. 1, i

Fig. 3 is a sectional view taken along the line 33 of Fig. 2, I v

Fig. 4 is a side view of an alternative cathode structure,

Fig. 5 is a face view of the structure of Fig. 4 with the front plateremoved, and

Fig. 6 is an enlarged sectional view taken along the line 66 of Fig. 5.

In the drawing an envelope 1 of glass or the like, which contains anydesired gas, such as neon, or source of vapor, such as mercury, orcombinations thereof, has sealed therein at one end the anodes 2 of ironor other suitable metal. At the opposite end of said envelope 1 is thecathode 3 which is formed either from a 'bimetallic strip wound in theform of a helix with the turns ly g in close proximity to each other, orfrom mblmetallic cylinder having a helical slot cut therein. 50 Theexterior metal of the cathode is preferably one, such as nickel, whichwill freely yield electrons when heated. The surface thereof is alsopreferably coated with alkaline or alkaline earth oxides to increase theelectronic emissivity. The inner end of said cathode 3 is rigidlysupported by the inlead 4, which is sealed through the endof theenvelope 1. At the opposite end said cathode 3 is loosely supported by aporcelain bushing 5 which is mounted upon a rigid inlead 6, being 1'held in position thereon in any suitable manner,

as by the cross wires 6' welded thereto. A metallic bridge 7 is weldedacross the interior end of the cathode 3, and serves as a lead andsupport for one end of a centrally disposed filament 8 of [3 tungsten orother suitable material. The other end of said filament 8 is welded tothe end of the inlead 6 adjacent to the bushing 5. The free end of thecathode 3 is bent outwardly and carries a contact 9. Another rigidinlead 10 terminates go in a contact 11 which is so located, as tocooperate with the contact 9 when said contact 9 reaches the positionoccupied by it when the cathode 3 is at operating temperature.

An auto-transformer 15 is connected by leads 5 16 and 17 to a suitablesource of alternating current. The end leads of said auto-transformer 15are each connected through a resistance 18 to one of the anodes 2throughthe leads 19. A mid-point of the transformer 15 is connectedthrough an iron cored inductance 20 to the inlead 4 of the gaseousdischarge device. One terminal of a low voltage secondary 21 is likewiseconnected to the inlead 4, While the other terminal thereof is connectedto the inlead 6. A connection is likewise made from the inlead 10 to oneterminal of a mercury switch 22, of the type commonly called a shifter.The other terminal of said shifter 22 is connected through a resistance23 to one of the leads l9. Said shifter 22 (which is only schematicallyshown) is normally in a circuit closing position, but has an armature inelectromagnetic relation to the core of inductance 20, so that whencurrent .flows through said inductance 20, said armature is attracted tosaid core and rotates said shifter to an open circuit position.

In the operation of this device an alternating potential is applied tothe leads 16 and 17, whereupon current immediately starts to flow fromthe 0 secondary 21 through inlead 4 to cathode 8, thence by bridge 7 tofilament 8 and through: inlead 6 back to said secondary 21. Normaloperating potential is likewise. impressed between each of the anodesand the cathode but is insufflcient to initiate the discharge. Thecurrent passing through the filament 8 heats up the cathode 3, causingthe lower end thereof to rotate because of its bimetallic construction,carrying the contact Steward the contact 11. ,When the cathode reachesits operating temperature the contact 9 is moved into engagement withsaid contact 11, completing the circuit from the mid-point oftransformer through inductance 20, inlead 4, cathode 3, contact 9,contact 11, inlead 10, shifter 22, resistance 23, part of a lead 19 anda resistance 18 back to one of the ends of transformer 15. Currentthereupon flows through said circuit, building up a strong magneticfield about the inductance 20. As said inductance 20 thus stores upenergy its core becomes magnetiaed, attracting the armature of shifter22, whereby the circuit is opened. As the magnetic field about saidinductance 20 collapses a high voltage ;surge is impressed upon thecathode 3, which tends to initiate a discharge to one of said anodes 2.If, for any reason, a discharge is not started the shifter 22 againcloses the circuit after the inductance 20 has become demagnetized andthe cycle is repeated until a discharge occurs, the discharge currentthan keeping shifter 22 in an open circuit position. Once a discharge isstarted it will be maintained by the potential difference existingbetween each of said anodes and said cathode. Since the cathode itselfis used to determine the first application of the high voltage surge itis obvious that the starting of the device will always occur at theproper time, regardless of variable atmospheric temperature, thetemperature of the cathode when the filament is eneropening in theinsulating member 25. The insulating member 25 is supported on rigidinleads 4 and 6 which pass through one of the short sides of saidinsulating member. Inlead 4 is con- A filament 29 is attached to the endof inlead 4 at one end and to the inlead 6 at the other end,

its midpoint being supported at the opposite end of the opening in theinsulating member 25. The ao cathode plate 27 is connected to the inlead10. "Centraliy located on the inner side of the cathode plate 26 is acontact 30, andcorrespondingly 10- e cated on the plate 27 is a contact31 which makes 1 contact with said contact 30 when the plates 5' 26, 27approach each other. Each of said cathode plates 26, 27, which may be ofthe same composition as the cathode 3 of Figs. 1-3, is curved slightlyoutward when cold, and has the material with'the greatest coefficient ofexpansion on the inner side. As the plates 26, 2'7 heat up under theinfluence of the filament 29 they will tend to bend inwardly, but sincethey are biased in the opposite direction this tendency results only inpotentialenergy which is stored 5 up in the form of internal stressesuntil the plates nected to the cathode plate 26 by the lead 28.

finally snap through their center line and bring the contacts 30, 31together, in a manner well known in the art. When this occurs cathodeplate 2'7 is so connected as to serve as a cathode during the operationof the device, and a circuit is made through inlead 4, lead 28, cathodeplate 26, contact 30, contact 31, cathode plate 27, and inlead 10 whichcorresponds to the circuit made from inlead 4 to inlead 10 in Fig. 1 bythe closing of the contacts 9 and 11. On" cooling of the cathodestructure the contacts 30, 31 are snapped apart after a time interval.This structure offers the obvious advantages of the snap 7 action inmaking and breaking the shifter circuit.

It is to be understoodthat the'structures shown "and described are forpurposes of illustration only, and thatthe invention can be embodied inother forms without departing from the spirit thereof. It will beobvious that expansion of the cathode structure can be availed of inmany ways to accomplish the same result, and that while shown inconnection with an alternating current device the invention is equallyapplicable to a direct current device.

I claim: g .7

1. In combination, a gaseous discharge device having a cathode ofrefractory solid material adapted to give off electrons when heated,means for heatingcsaid cathode, means for a discharge within said deviceand means responsive'to temperature changes in said cathode for delayingthe operation of said means for initiating a discharge until saidcathode has reached an. operating temperature.

2. In combination, a gaseous discharge device having a cathode "ofrefractory solid material adapted to give off electrons when heated,means for heating said cathode, means for applying a. voltage surge tosaid discharge device, and means responsive to temperature changesinsaid cathode for delaying said voltage surge until said cathode hasreached an operating temperature. 1

i' 3. In combination, a gaseous discharge device having a cathode ofrefractory solid material adapted to give off electrons when heated,means for heating said cathode, means for initiating a discharge withinsaid device and means responsive to thermal expansion of said cathode todelay the operation of said means for initiating a discharge until saidcathode has reached an operating temperature.

4. In combination, a gaseous discharge device having a cathode adaptedto give off electrons when .heated, means for heating said cathode,means for applying a voltage sin-ge to said discharge device, said lastmentioned means including an element responsive to thermal expansion ofsaid cathode to control energization of said surge applying means.

5. In combination, a gaseous discharge device having a cathode ofrefractory solid material adapted to emit electrons when heated, meansfor heating said cathode, means to initiate a iiischarge through saiddevice, said last mentioned means being normally inoperative, and meansoperated by thermal expansion of said cathode to render said dischargeinitiating means operative when said cathode has reached a-temperatureat which the free electron emission therefrom will support the normaldischarge current.

6. In combination, a gaseous discharge device having a cathode adaptedto emit electrons when heated. means for heating said cathode, means forapplying a voltage surge to said device, said means being normallyinoperative, and means sive to temperature changes in said cathode fordelaying the operation of said means for initiating a discharge untilsaid cathode has reached a temperature at which the free electronemission therefrom will support the normal discharge current.

LEROY J. BUTI'OLPH.

